JP2006048420A - Method for preparing color conversion table, and image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively shorten retrieving time of a point where the color difference from a target color corresponding to a lattice point becomes minimum in the preparation of a color conversion table. <P>SOLUTION: By using the first preceding color processing table which is previously prepared, a succeeding RGB value 501 corresponding to a target color of a prescribed lattice point constituting the second preceding color conversion table is found out by interpolation calculation. Namely interpolating operation using respective lattice point data (succeeding RGB values) of a plurality of lattice points around the first preceding color processing table is performed in accordance with a position in the first preceding color processing table that is occupied by the prescribed lattice point which is a noticed lattice point concerned with processing, and then the succeeding RGB value 501 corresponding to the notices lattice point is found out. Then a nearby area 502 to the obtained succeeding RGB value 501 is set and the succeeding RGB value 503 most approximate to the target color is found out from all succeeding RGB values included in the nearby area 502 as the lattice point data of the noticed lattice point. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color conversion table creation method and an information processing apparatus. More specifically, the present invention relates to a lookup table (hereinafter referred to simply as “LUT”) used in color conversion processing, which is processing for generating data used in an image output device such as a printer. Is also related to an image processing apparatus that executes the creation process.

  In image output by an inkjet printer or the like, generally, color conversion processing is performed to convert image data of an input color signal from an image input device into image data of an output color signal for use in a printer that is an image output device, and output data. Is generated. The input color signal is defined as a color in a device color space (for example, RGB color space) depending on the image input device, while the output signal is defined as a color in a device color space (for example, CMYK or RGB) depending on the image output device. Is done. Therefore, in the color conversion processing, processing for converting the device color space of the input color signal into the color space of the output color signal is performed. Conventionally, color conversion from the device color space of the input device to the device color space of the output device has been realized by matrix calculation or the like, but in recent years it has been performed using a three-dimensional LUT for more accurate conversion. There are many cases.

  As one aspect of color conversion as described above, color conversion relating to color reproducibility (or color gamut reproducibility) is performed. For example, there are various color reproducibility such as color reproducibility emphasizing gradation, color reproducibility emphasizing saturation, color reproducibility emphasizing colorimetric matching, and color reproducibility emphasizing memory colors. In one conventional example, a plurality of LUTs corresponding to such a plurality of color reproducibility are prepared, and color conversion is performed by selecting the LUT according to the type of image to be output. As a result, color reproduction suitable for the output image can be realized. In addition, in order to maintain this color reproducibility, color conversion from the color space of the input device to the color space of the output device, pre-stage color conversion (color correction) that performs conversion related to color gamut mapping, and recording of ink, etc. There are cases where the control is divided into two, that is, post-stage color correction (color separation) for performing color separation processing on the agent data.

  As an input color space generally used for defining image data, for example, many color spaces such as sRGB, AdobeRGB, and NTSC are known in the RGB system. In order to perform color conversion from the device color space of the input device to the device color space of the output device corresponding to such multiple input color spaces, the color conversion between them is performed for each combination of input / output devices. It is necessary to provide an LUT that defines On the other hand, a color conversion method using an ICC profile that can perform color conversion regardless of the combination of input / output devices is also known. The ICC profile defines color conversion from an input color space to a device-independent color space (for example, XYZ, Lab, etc.) corresponding to an input device, and similarly, corresponding to an output device. The color conversion from the device-independent color space to the device color space of the output device is defined. Specifically, the color conversion defined by the profile is realized by the LUT as described above. In color conversion using an ICC profile, each input / output device may basically prepare one profile that defines the conversion relationship with a device-independent color space. The color conversion of the device color space between the input / output devices can be performed by combining the profiles of the respective devices. In the ICC profile, an LUT having three types of characteristics: color reproducibility that emphasizes gradation, color reproducibility that emphasizes saturation, and color reproducibility that emphasizes colorimetric matching is included in one profile. keeping.

  Specifies the color conversion relationship between the LUT or the device-independent color space of the input / output device and the LUT when performing direct color conversion from the device color space of the input device to the device color space of the output device. The creation of any LUT as a profile to be performed is performed as follows.

  First, the target color corresponding to the grid point constituting the LUT to be created is determined, and then the device color of the output device that is closest to the target color (for example, the latter stage RGB (the RGB obtained by the previous stage color conversion described above) ) Or CYMK), and the corresponding color of the lattice point, that is, lattice point data is used. In general, the target color and the device color based on the target color are defined in a uniform color space (Lab or Luv).

  Specifically, first, based on the subsequent stage RGB (or CMYK), which is a color signal in the device color space of the printer, a predetermined number of color patches are output by the printer, and the color patches are measured to obtain a color. A color signal in a uniform color space corresponding to the patch is obtained. Thereby, the relationship between the latter-stage RGB value (or CMYK value) and the Lab value (or Luv value or the like) of the uniform color space can be obtained. When obtaining the relationship from the latter RGB value to the Lab value, the accuracy increases as the number of samples such as color patches increases. However, it is unrealistic to print out all the colors in the RGB color space as samples. Is. Therefore, for example, a color patch having the same distance in the device color space of the printer is output, and the color is measured to obtain the relationship between the subsequent RGB value and the Lab value. Accordingly, a table from the printer-dependent color space to the uniform color space (hereinafter referred to as “color space correspondence table”) is obtained. For colors other than the color indicated by the subsequent RGB value for outputting the color patch (the subsequent RGB value), the Lab value is estimated by a known interpolation operation such as tetrahedral interpolation using this color space correspondence table. A relationship can be sought.

  Next, the target color (Lab value) corresponding to the target grid point constituting the LUT to be created is compared with Lab values corresponding to all subsequent RGB values in the color space correspondence table, and the color difference is minimized. By searching for the most approximate point as a point, the subsequent RGB value of the most approximate point can be obtained as the corresponding color of the grid point of interest, that is, grid point data.

  However, in this case, it takes an enormous time to search for all subsequent RGB values. Therefore, a method described in Patent Document 1 has also been proposed to reduce search time. In this document, first, a point at which the color difference from the target color is minimized is searched from the subsequent RGB values corresponding to the color patches actually measured. Next, a point that can be approximated as a point having a minimum color difference from the target color is searched from the subsequent RGB values in the vicinity of the subsequent RGB values, and the subsequent RGB values are used as the corresponding colors of the grid points. Thus, the search time is reduced by reducing the search range.

Japanese Patent No. 3371964

  However, even the method considering reduction in search time as described in Patent Document 1 still has room for reduction in search time, and it cannot be said that the search time is sufficiently reduced. That is, in Patent Document 1, in order to avoid searching for all the subsequent RGB values, a point where the color difference from the target color is the smallest among the subsequent RGB values corresponding to the color patches actually measured. Although the search process is performed, the search is not changed, and a certain amount of time is required.

  In addition, the neighborhood area that needs to be searched must include an intermediate point between the grid point that minimizes the color difference and the adjacent grid point, and the neighborhood to be searched depends on the number of grid points in the color space correspondence table. A region is determined. The search time can be reduced by reducing the neighborhood area, but the neighborhood area cannot be reduced alone, and the number of grid points must be increased to reduce the neighborhood area. Cannot be realized effectively.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to effectively reduce the search time for a point where the color difference from the target color corresponding to the grid point is minimized. It is an object of the present invention to provide a color conversion table creation method and an image processing apparatus that make it possible.

  Therefore, in the present invention, a method for creating a color conversion table for converting an input color signal value into an output color signal value, the first color conversion table for converting an input color signal value into an output color signal value, and A step of preparing a color space correspondence table for converting the color space of the output color signal value into another predetermined color space, and the target color determined for the grid points of the color conversion table according to the creation A step of obtaining a corresponding output color signal value by interpolation calculation in the first color conversion table, and setting a neighborhood region of the obtained output signal value, and an output color signal closest to the target color in the set neighborhood region A step of obtaining a value using the color space correspondence table, and a step of setting the obtained output signal value in lattice point data of lattice points of the color conversion table according to the creation, You .

  An image processing apparatus for creating a color conversion table for converting an input color signal value into an output color signal value, the first color conversion table for converting an input color signal value into an output color signal value; A color space correspondence table for converting the color space of the output color signal value into another predetermined color space, and an output color signal value corresponding to the target color determined for the grid points of the color conversion table according to the creation And means for calculating by interpolation calculation in the first color conversion table, and setting a neighborhood area of the obtained output signal value, and setting an output color signal value closest to the target color in the set neighborhood area to the color space Means for obtaining using a table, and means for setting the obtained output signal value to lattice point data of lattice points of the color conversion table according to the creation.

  According to the above configuration, the output color signal value corresponding to the target color determined for the grid point of the color conversion table according to the creation is obtained by the interpolation calculation in the first color conversion table, and the vicinity region of the obtained output signal value The output color signal value closest to the target color in the set neighborhood region is obtained using the color space correspondence table, and the obtained output signal value is obtained as the lattice point data of the lattice point of the color conversion table according to the creation. Therefore, it is not necessary to first search for the output color signal value when obtaining the output color signal value corresponding to the target color.

  As a result, the search time for creating the color conversion table can be greatly reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a block diagram showing a schematic configuration of an image output system according to an embodiment of the present invention.

  In FIG. 1, a host computer 100 such as a personal computer is issued to an OS 102 from an operating system (OS) 102 and application software 101 such as a word processor, spreadsheet, and Internet browser that operate based on the operating system (OS) 102. A printer driver 103 that creates various print command groups (image drawing command, text drawing command, graphics drawing command, etc.) and creates print data representing an output image, and a monitor driver that creates image data to be displayed on the monitor 106 104 or other software.

  The host computer 100 includes a CPU 108, a hard disk drive (HDD) 107, a RAM 109, a ROM 110, and the like as various hardware for operating these software. As a configuration shown in FIG. 1, a personal computer 100 in which Windows (registered trademark) is an OS 102 and installed as arbitrary application software 101 having a printing function is conceivable. Further, for example, an inkjet printer can be used as the printer 106, and a CRT or LCD can be used as the monitor 106, respectively.

  The application software 101 of the host computer 100 is based on the image displayed on the monitor 106, text data classified into text such as characters, graphics data classified into graphics such as graphics, and image data classified into photographic images. The output image data to be printed is created using the above. When the output image is printed, a print request is issued from the application software 101 to the OS 102, the text data portion is a text drawing command, the graphics data portion is a graphics drawing command, and the image data portion is a drawing configured as an image drawing command. A group of instructions is sent to the OS 102. When the OS 102 receives the print request, the OS 102 passes a drawing command group to the printer driver 103 corresponding to the printer that is to execute printing. The printer driver 103 processes a print request and a drawing command group input from the OS 102, creates print data that can be printed by the printer 104, and transfers the print data to the printer 104.

  When the printer 104 is a raster printer, the printer driver 103 sequentially performs image correction processing on the rendering command group, and rasterizes the image in an RGB 24-bit page memory. After all the rendering commands are rasterized, the printer driver 103 converts the RGB data stored in the page memory into a data format that can be printed by the printer 104, for example, CMYK data, and transfers the CMYK data to the printer 104.

  FIG. 2 is a diagram illustrating processing performed by the printer driver 103 illustrated in FIG.

  In FIG. 2, an image correction processing unit 201 performs image correction processing on color information included in a drawing command group input from the OS 102. For example, after converting the color information of the device color space (for example, RGB) of the image input device into a luminance / color difference signal and subjecting the luminance signal to exposure correction processing, the corrected luminance / color difference signal is again converted to the device color of the input device. A process of performing inverse conversion to the RGB color information of the space is performed.

  The printer correction processing unit 202 refers to the RGB color information of the device color space of the input device subjected to the image correction processing as described above, rasterizes the image based on the drawing command, and generates a raster image on the page memory. . For this raster image, preceding color signal conversion (color conversion from the device color space of the input device maintaining color reproducibility to the device color space of the output device), subsequent color signal conversion (color separation into CMYK), and Processing such as gradation correction is performed to generate CMYK data for determining the color reproducibility of the printer 105 for each pixel.

  The processing described with reference to FIG. 2 has been described as processing performed by the printer driver 103, but may be performed by an application.

FIG. 3 is a diagram for explaining in detail the processing of the printer correction processing unit 202 shown in FIG.
In FIG. 3, the image data input by the image signal input unit 301 includes input color matching processing in the preceding color signal processing unit 302, color separation processing in consideration of the characteristics of the ink jet printer in the subsequent color signal processing unit 303, and gradation. Tone correction and halftone processing are performed in the correction unit 304, and cyan (C), magenta (M), yellow (Y), black (K), light cyan (c), and light magenta (m) used in the printer 104 are used. C, M, Y, K, c, and m dot data corresponding to each of the inks are generated. Then, the image output unit 305 transfers these dot data to the printer 104 at a timing according to the printing operation in the printer 104. In the printer correction processing unit 202 described above, the LUT used in the preceding color signal conversion unit is created by table creation processing described later with reference to FIGS.

  In the present embodiment, the printer 104 uses a total of six colors of inks C, M, Y, and K having normal densities and light inks c and m having lower densities than the inks C and M, respectively. In the post-stage color signal processing, color separation is performed in consideration of the granularity of printed dots in the printer and the total ink droplet amount that the recording medium can accept per unit time and unit area. The LUT used in the post-stage color processing unit 303 is set so that RGB data is color-separated and an appropriate combination of C, M, Y, K, c, and m inks is output in consideration of these conditions. . As described above, if the color processing of the printer is operated via the post-stage color processing unit 303, it is not affected by the configuration of the printer, for example, the configuration of 4 colors of CMYK or 6 colors of CMYKcm. The printer can be handled as an RGB device that simply processes RGB data. The RGB data at this time will be referred to as subsequent RGB. Specifically, the RGB data output from the previous color signal processing unit 302 is the subsequent RGB.

  The LUT (hereinafter also referred to as a pre-stage color processing table) used in the pre-stage color signal processing unit 302 performs color conversion from the device color space (RGB color space) of the image input device to the device color space (post-stage RGB) of the output device. This is a three-dimensional LUT. In this embodiment, regarding color reproduction characteristics, color reproduction with emphasis on gradation, color reproduction with emphasis on saturation, color reproduction with emphasis on colorimetric matching, and color reproduction with emphasis on memory colors. A corresponding preceding color processing table is prepared, and the preceding color processing table to be used is selected according to the image to be printed. Since these tables correspond to the device color spaces of other input devices, there may be as many pre-processing tables as the number of corresponding color spaces.

  Next, a process for creating the previous color processing table will be described.

  In this creation process, first, a target color corresponding to a predetermined grid point constituting the previous color processing table to be created is determined, a subsequent RGB value closest to the target color is obtained, and a corresponding color of the grid point is determined. That is, the grid point data is used. Here, the target color is defined as a value of the color space Lab which is a uniform color space. Specifically, in the LUT to be created, for each color (grid point) defined by the input RGB values, colors outside the printer's color gamut are also included, so color gamut compression according to the color reproducibility to be created The color (Lab value) obtained by performing is set as the target color. The LUT of the previous color processing table is created by obtaining the grid point data of the grid point corresponding to the target color for each grid point.

  As yet another method, the target color is each color (grid point) defined by the input RGB values in the LUT to be created, for example, some predetermined colors such as a line connecting white-red-black. Is a color (Lab value) determined in consideration of the color gamut characteristics and the like. When the lattice point data of the lattice point corresponding to the target color is obtained, the lattice point data (rear stage RGB value) of the predetermined lattice point obtained in this way is then used to perform interpolation calculation of other lattice points. Lattice point data is obtained and an LUT for the previous color processing table is created.

  More specifically, first, color patches are printed at a predetermined combination of appropriate sampling intervals of the subsequent stage RGB data, and the color patches are measured by a colorimeter such as Spectrolino manufactured by Gretag, for example. Then, from the color measurement result, a color space correspondence table indicating the correspondence from the subsequent RGB value to the Lab value is obtained. That is, the grid points in this table are defined by RGB values, and the grid point data is Lab values. Inkjet printers print patches and use the colorimetric results for color development due to complex and diverse factors such as color change due to ink color mixing and color change due to ink penetration into the recording medium. This is because it is difficult to predict the color development characteristics. By performing an interpolation operation using the color space correspondence table obtained as described above, a Lab value corresponding to an arbitrary subsequent RGB value can be obtained.

  Next, the target color corresponding to the grid point constituting the previous color processing table to be created is compared with the Lab value associated with the subsequent RGB value by the color space correspondence table, and the color difference is minimized. Find a point that can be approximated. Then, the RGB value that minimizes the color difference is used as the corresponding color of the grid point constituting the previous color processing table, that is, grid point data. By performing the above processing in the same manner for the predetermined grid points constituting the previous color processing table, the grid point data can be obtained for the grid points of a plurality of predetermined lines in the previous color processing table.

  FIG. 4 is a diagram illustrating a table creation method described in Patent Document 1 for comparison regarding table creation. The grid points of the table are arranged in a three-dimensional array, but will be described as a two-dimensional array for the sake of simplicity.

  In FIG. 4, reference numeral 401 denotes a grid point constituting a color space correspondence table that defines the correspondence from the subsequent RGB to the Lab value. Reference numeral 402 denotes a Lab value that is a target color of a grid point constituting the preceding color processing color table. That is, FIG. 4 shows both the grid points of the color space correspondence table and the color positions (Lab values) in the Lab color space at the same time.

  In the table creation method described in Patent Document 1, first, a lattice point that minimizes the color difference between the Lab value, which is the lattice point data, and the target color is searched from among lattice points constituting the color space correspondence table ( First search). It is assumed that the minimum color difference grid point obtained in this way is the grid point 403.

  Next, a neighborhood region 404 of the subsequent RGB values to be searched is set, and an approximate point that minimizes the color difference between the corresponding Lab value and the target color is searched from the subsequent RGB values of the neighborhood region (second Search), and that point (the latter RGB value) is used as the grid point data of the grid point of interest. The corresponding point thus obtained is indicated by 405.

  Here, when the latter stage RGB is defined by 0 to 255, and the number of grid points constituting the color space correspondence table from the latter stage RGB to the Lab value is 9 × 9 × 9, the search is performed in the first search. The number of grid points to be performed is 9 × 9 × 9 = 729. In the second search, the neighboring area to be searched must include an intermediate value between the lattice points. Therefore, when the distance between the lattice points is 32, it is necessary to search for an area having the distance 16 from the lattice point. There is. Therefore, in the second search, the neighborhood area to be searched is at least 33 × 33 × 33. As another example, when the number of grid points constituting the color space correspondence table is 17 × 17 × 17, the number of grid points searched in the first search is 17 × 17 × 17 = 4913. In this case, the neighborhood area to be searched in the second search is at least a range of 17 × 17 × 17.

FIG. 5 is a diagram for explaining the pre-color processing table creation process according to the present embodiment.
In this embodiment, first, a first previous color processing table is prepared in advance. That is, in the present embodiment, as described above, a plurality of pre-stage color processing tables are created regarding the color reproduction characteristics. In that case, the table creation method according to the embodiment of the present invention is applied to the creation of the second and subsequent pre-stage color processing tables. Therefore, the first previous color processing table may be created using any of the methods conventionally known in Patent Document 1 or the like.

  In FIG. 5, reference numeral 401 denotes a grid point that forms a color space correspondence table that defines the relationship from the subsequent RGB to the Lab value. Reference numeral 402 denotes a Lab value that is a target color of a grid point constituting the second previous-stage color processing table to be created. That is, FIG. 5 shows both the grid points of the color space correspondence table and the color positions (Lab values) in the Lab color space at the same time as in FIG.

  First, using a first pre-stage color processing table created in advance, for a predetermined grid point constituting the second pre-stage color process table, a post-stage RGB value 501 corresponding to the target color of the grid point is interpolated. Calculate by calculation. That is, in accordance with the position occupied by the predetermined grid point, which is the target grid point related to the process, in the first previous color processing table, the grid point data (the subsequent RGB value) of each of the plurality of grid points around the table Is used to obtain a subsequent RGB value 501 corresponding to the grid point of interest.

  Next, the neighborhood region 502 is set for the obtained downstream RGB value 501, and the subsequent RGB value 503 that most closely approximates the target color from all the downstream RGB values included in the neighborhood region 502 is set as the target grid point. Is obtained as grid point data.

  The above processing is performed for all of the predetermined lattice points to obtain lattice point data, and for other lattice points, interpolation processing using the predetermined lattice point data is performed to obtain those lattice point data. A first previous color processing table can be created.

  Further, the third and subsequent pre-color processing tables can be obtained in the same manner as described above.

  As described above, in the method of the present embodiment for creating the second and subsequent pre-stage color processing tables, the grid points constituting the color space correspondence table from the post-stage RGB to the Lab value, compared to the method described in Patent Document 1. It is not necessary to execute the first search for searching for a lattice point having the smallest color difference from the target value from Thereby, when the number of grid points constituting the color space correspondence table is 9 × 9 × 9, 9 × 9 × 9 = 729 for one target value, and the number of grid points is 17 × 17. In the case of × 17, it is not necessary to search for 17 × 17 × 17 = 4913, and the search time can be greatly reduced.

  More preferably, the first pre-stage color processing color table is a table that realizes color reproducibility with an emphasis on colorimetric matching. In other words, this table shows color reproduction characteristics such that the target value of the grid point at the time of creation is set so as to match the colorimetric value of the patch printed by the subsequent RGB value that is the grid point data. I have it. When the first-stage color processing table having color reproducibility with an emphasis on colorimetric matching is used as the first table, the second-stage RGB closest to the grid point data of the grid point corresponding to the target value is obtained by interpolation processing in the table. The value can be determined directly. However, since the interpolation error due to the interpolation processing is included, the obtained subsequent RGB value is less accurate than the subsequent RGB value obtained using the LUT from the device-dependent color space of the output device to the uniform color space. However, the Lab value of the post-stage RGB value 501 obtained by the interpolation calculation for the grid points constituting the second and subsequent pre-stage color processing tables is a value relatively close to the Lab value of the target color corresponding to the target grid point. There is a high possibility that the signal value 503 having the minimum color difference exists very close to the obtained post-stage RGB value 501. As described above, by using a table that realizes color reproducibility with an emphasis on colorimetric matching as the first preceding color processing table, it is possible to reduce the neighborhood range to be searched in the second search. As a result, in the case of the method described in Patent Document 1, the number of grid points constituting the color space correspondence table is 9 × 9 × 9, the neighboring region is 33 × 33 × 33, and the number of grid points is another example. Is 17 × 17 × 17 and the neighboring area is 7 × 17 × 17, but this range can be greatly reduced.

  FIG. 6 is a block diagram illustrating functions of the image processing apparatus that creates the previous-stage color processing table according to the present embodiment.

  The image processing apparatus according to this embodiment includes a first LUT holding unit 602 that holds a first LUT that is a first pre-stage color processing table in which a device color space of an input device and a device color space of an output device that are created in advance are associated with each other. A color space correspondence LUT holding unit 603 that holds a color space correspondence table that associates the device color space of the output device with the uniform color space, and a creation that holds the target colors (values) of the grid points constituting the pre-stage color processing table to be created An LUT target value holding unit 601 is provided. Then, the LUT calculation unit 604 interpolates and calculates the color signal value of the device color space of the output device corresponding to the target color using the first LUT. Further, the neighborhood area search unit 605 outputs the device color space of the output device that is the closest to the target color from all the color signal values in the neighborhood area with respect to the color signal value of the device color space of the output device obtained by interpolation. Are obtained using the color space correspondence LUT, and the pre-stage color processing table 606 is created.

(Embodiment 2)
In the first embodiment, the method for creating the pre-stage color conversion table, which is color conversion from the device color space of the input device to the device color space (post-stage RGB) of the output device, has been described. It can be used in a method for creating a color signal conversion table that directly converts from the device color space of the input device to the device color space (CYMK) of the output device, instead of a processing system that performs one color conversion. Is also obvious.

(Embodiment 3)
In the first and second embodiments, the method for creating a color conversion table from the device color space of the input device to the device color space of the output device (the subsequent stage RGB or CMYK) has been described, but it is used in color conversion using an ICC profile. It can also be used in a method of creating a color conversion table from a device-independent color space (XYZ or Lab) to a device color space (subsequent RGB or CMYK) of an output device.

(Embodiment 4)
In the first to third embodiments, the method for creating the color conversion table has been described. However, when the preceding color signal processing unit 302 performs an interpolation operation in the previous color processing table for converting the previous color signal to the subsequent color signal, the embodiment is described. By using the method for estimating the post-stage RGB value described in 1, the conversion accuracy of the post-stage color signal value obtained by the pre-stage color signal processing unit 302 can be improved. In other words, the preceding-stage color processing table is used as the first table, and this and the color space correspondence table prepared in advance can be used to estimate the latter-stage RGB value as the interpolation result.

(Embodiment 5)
In the first to fourth embodiments, it is described that a series of processing is performed on the host computer 100. However, the printer 104 has the same function as the host computer 100, and the above-described series of processing is performed on the printer 104. It is also possible to do.

  For example, when a function equivalent to that of the host computer 100 is provided inside the printer, the image data is read from an image input device such as a digital camera from a reading means such as a card reader provided in the printer via a memory card, or digitally. It is possible to read out from a memory card or a built-in memory held by the digital camera by connecting the camera and printer with a wired cable, infrared communication means, or wireless means.

(Embodiment 6)
The present invention can be realized by supplying a processing program as software to another computer. In this case, for example, processing for realizing the present invention using a recording medium such as a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, and a ROM. A program can be supplied.

1 is a block diagram showing a schematic configuration of an image output system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating processing performed by a printer driver 103 illustrated in FIG. 1. It is a figure explaining the process of the correction process part 202 for printers shown in FIG. 2 in detail. It is a figure explaining the table preparation method as described in one prior art example for the comparison regarding table preparation. It is a figure explaining the preparation process of the front | former stage color processing table which concerns on one Embodiment of this invention. It is a block diagram which shows the function of the image processing apparatus which produces the front | former stage color processing table which concerns on one Embodiment of this invention.

Explanation of symbols

100 Host computer 101 Application 102 OS
103 Printer driver 104 Printer 107 HD
108 CPU
109 RAM
110 ROM
DESCRIPTION OF SYMBOLS 201 Image correction process part 202 Printer correction process part 301 Image signal input part 302 Previous stage color signal process part 303 Rear stage color signal process part 304 Gradation correction part 305 Image output part 601 Creation LUT target value holding part 602 First LUT hold part 603 Color space-corresponding LUT holding unit 604 LUT calculation unit 605 Neighboring region search unit 606 Creation LUT

Claims (10)

A method for creating a color conversion table for converting an input color signal value into an output color signal value,
A first color conversion table for converting an input color signal value into an output color signal value and a color space correspondence table for converting a color space of the output color signal value into another predetermined color space are prepared. And a process of
Obtaining an output color signal value corresponding to a target color defined for a grid point of the color conversion table according to the creation by interpolation calculation in the first color conversion table;
Setting a neighborhood region of the obtained output signal value, and obtaining an output color signal value closest to the target color in the set neighborhood region using the color space correspondence table;
Setting the obtained output signal value to grid point data of grid points of the color conversion table according to the creation;
A color conversion table creation method characterized by comprising:   The predetermined color space is a uniform color space, and the first color conversion table is a color conversion table in which the output color signal value has a color reproduction with a colorimetric match. Color conversion table creation method.   The color conversion table creation method according to claim 1 or 2, wherein the color conversion table performs conversion from a device color space of an input device to a device color space of an output device.   The color conversion table creation method according to claim 1, wherein the color conversion table performs conversion from a device-independent color space to a device color space of an output device. An image processing apparatus for creating a color conversion table for converting an input color signal value into an output color signal value,
A first color conversion table for converting input color signal values into output color signal values;
A color space correspondence table for converting the color space of the output color signal value into another predetermined color space;
Means for obtaining an output color signal value corresponding to a target color defined for a grid point of the color conversion table according to the creation by interpolation calculation in the first color conversion table;
Means for setting a neighborhood region of the obtained output signal value and obtaining an output color signal value closest to a target color in the set neighborhood region using the color space correspondence table;
Means for setting the obtained output signal value to grid point data of grid points of the color conversion table according to the creation;
An image processing apparatus comprising:   6. The predetermined color space is a uniform color space, and the first color conversion table is a color conversion table in which the output color signal value has a color reproduction with a colorimetric match. Image processing device.   The image processing apparatus according to claim 5, wherein the color conversion table performs conversion from a device color space of an input device to a device color space of an output device.   The image processing apparatus according to claim 5 or 6, wherein the color conversion table performs conversion from a device-independent color space to a device color space of an output device. A color estimation method for estimating an output color signal by an interpolation operation using a color conversion table for converting an input color signal value to an output color signal value,
A first color conversion table for converting an input color signal value into an output color signal value and a color space correspondence table for converting a color space of the output color signal value into another predetermined color space are prepared. And a process of
Obtaining an output color signal value corresponding to a target color defined for a grid point of the color conversion table according to the creation by interpolation calculation in the first color conversion table;
Setting a neighborhood region of the obtained output signal value, and obtaining an output color signal value closest to the target color in the set neighborhood region using the color space correspondence table;
A color estimation method characterized by comprising: A program for executing a process of creating a color conversion table for converting an input color signal value into an output color signal value, and a first color conversion table for converting an input color signal value into an output color signal value And a color space correspondence table for converting the color space of the output color signal value into another predetermined color space,
Means for obtaining an output color signal value corresponding to a target color defined for a grid point of the color conversion table according to the creation by interpolation calculation in the first color conversion table;
Means for setting a neighborhood region of the obtained output signal value and obtaining an output color signal value closest to a target color in the set neighborhood region using the color space correspondence table;
Means for setting the obtained output signal value to grid point data of grid points of the color conversion table according to the creation;
A program characterized by functioning as

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